Fine grain iron and method of production



Patenteol July 13, 1954 UHTED STATES ATENT OFFICE FINE GRAIN IRON ANDMETHOD OF PRODUCTION ration of Delaware No Drawing. Application October31, 1951, Serial No. 254,191

10 Claims.

The invention relates to a method for the production of iron and steelsand to the products obtained thereby, and includes correlatedimprovements and discoveries whereby the properties of iron and steelare decidedly improved.

Further, the procedure may be employed with killed steel of alloy or ofcarbon grades, and the steel may be manufactured by conventionalmethods.

Steels, in the course of their manufacture absorb certain undesirablegases and substances which may impart oor engineering properties and maymake the material difficult to shape or work.

A principal object of the invention is to provide a method whereby theforegoing disadvantages may be substantially wholly obviated.

A further object of the invention is to provide a method in accordancewith which an iron and steel may be produced as a fine grain product,and having distinctive corrosion and oxidation resistance and highimpact values at room and at low temperatures.

Another object of the invention is to provide a process for themanufacture of a steel having a relatively lowered sulphur content, andwith respect to which the nitrogen content has been eliminated ormaterially reduced.

A particular object of the invention is the provision of a methodwhereby the foregoing are achieved, and a product, namely an iron or asteel of enhanced properties, is obtained through the utilization of acomposition containing a rare earth metal, preferably a plurality ofrare earth metals with cerium being present'in a preponderant amount.

Other objects of the invention will in part be obvious and will in partappear hereinafter.

For the production of a steel which is highly resistant to corrosion andoxidation, there are two generally accepted methods.

One method utilizes one or more of a number of commonly accepted alloys,and usually a minimum of 12% is employed. These alloys contain a memberof the group consisting of molybdenum, chromium, nickel, cobalt,titanium, tantalum, columbium and zirconium with varying amounts ofsilicon, copper, aluminum and manganese.

The second method uses the minimum amount of those metals and produces agrain in which the interstitial spaces are reduced in size and, thus,

2 reduce the opportunity for corrosive and oxidation agents to attackthe steel.

In view of the fact that the alloys which are usually employed inproducing alloy and carbon grade steels are in great demand and as suchare hard to obtain at all times, we decided to attempt to improve thesetypes by producing a fine grain in the steel and to do this the moltensteel has been treated with an alloy which is made up essentially ofmetals of the rare earth group.

The invention accordingly comprises the several steps and the relationof one or more of such steps with respect to each of the others, and theiron or steel possessing the features and properties, which areexemplified in the following detailed disclosure, and the scope of theinvention will be indicated in the claims.

In the practice of the invention, the properties of iron and steel,especially regular alloy and carbon grades, e. g, 4300; 2300 and 3100 anumber of which are known as S. A. E. types, and other alloy-steelvarieties designated as constructional steels, are decidedly improved bythe addition of an appropriate amount of a composition containing a rareearth metal, either singly or in compatible combination, and suitablythat which is now known in the trade, and which we designate herein asL-metal which contains a mixture of rare earth metals, and suitablycontaining a preponderant amount of cerium and of the followingapproximate percentage composition: cerium 50.00; lanthanum 30.00 andthe balance various rare earth metals as praseodymium, samarium,neodymium, etc, and iron, to a melt, that is to the liquid iron orsteel.

More especially, the procedure comprises preparing an iron containingmelt, adding metallics, which may contain chromium, manganese,molybdenum, nickel, columbium, titanium, tantalum, cobalt, zirconium andsilicon, thereto during furnacing, deoxidizing utilizing e. g. ierrosilicon, calcium silicon, ferro manganese, and the like, and then addingthe composition which, more particularly, contains a plurality of rareearth metals having cerium present in a preponderant amount.

While the addition of the rare earth metal may be eiiected at difierentphases of the melting and furnacing, a suitable procedure is to add itto the ladle either before or after deoxidizers havebeen added, anddesirably before the ladle is onehalf full, that is while the ladle isless than one- 3 half full. However. another and somewhat preferredprocedure is to place the material in the bottom of a ladle and coverover with a deoxidizer such as calcium silicide, or it may be placed ina thick walled pipe and the ends closed, and then placed in the bottomof the ladle where the liquid ferrous metal may be poured on top of it.Either method delays the action of the L-metal so that there will besuflicient liquid metal to allow a proper reaction therewith.

Further, we have found that when about 3 pounds of the L-metal, or itsequivalent, have been added per ton of iron or steel a very fine grainstructure results. However, depending on the pouring temperature, thesize of the mold, and the analysis desired, an amount of about 1 poundof the L-metal to the ton has given beneficial results.

In the manufacture, the usual accepted good practice is employed and inaddition to it, care is taken to see that the melt is properlydeoxidized, that is, poured at a temperature which has been found to belower than usual practice because of the fact that the treatment withthe rare earth metal seemingly increases the fluidity of the treatedmetal.

Various quantities of rare earth metal have been tried and found to beeffective. However, when excessive amounts of the metal have been added,the product has been found to be extremely dirty and as such offered lowresistance to oxidation or corrosion. Our method makes eflicient use ofthe L-metal and at the same time utilizes only a very small amount. Wehave definitely found that not more than three pounds of L-metal per tonneed be used provided that it is added to the melt as herein describedand especially in the preferred manner.

As an illustrative embodiment of a manner in which the method may becarried out, the following example is presented:

A heat of a manganese-molybdenum steel was made having the followinganalysis expressed as percentages:

Carbon 0.30 Manganese 1.80 Sulfur 0.024 Phosphorus 0020 Silicon 0.26Molybdenum 0.47 Rare earth metal, the remainder iron 0.005

The charge consisted of:

Pounds Scrap 4,500 Pig iron 4,200

ter the melt had been formed and during furnacing, there were added:

Pounds Molybdenum oxide (M003) 75 Spar Scale 10 Ferro Silicon (75% FeSi)60 Ferro Manganese (82% Mn) 190 To the ladle, prior to and duringpouring, and suitably prior to the ladle being half full, there wereadded:

Pounds Ferro Manganese (85% Mn) 95 Alsifer 26 Grainal 17 CalciumSilicide 12 L-metal 8 Alsifer is a carbonless alloy of aluminum, siliconand iron having the following approximate composition: aluminum 20%;silicon 40%, and iron 40%. Grainal is an alloy containing aluminum,zirconium, titanium and boron of the following approximate percentagecomposition; aluminum 13.00; titanium 20.00; zirconium 4.00; manganese8.00; boron 0.50; silicon 5.00; and the balance iron.

The slag was held back and the heat was tapped after a short interval,and. the pouring temperature was about 2690 F. The ingots were permittedto stand for about one hour after which they were stripped and placed inthe soakin'g pits. After a period of 10 to 12 hours the ingots werecooled on a strip mill to billet size, and a thorough examination showedthat the edges were not cracked.

Steels produced by the foregoing procedure may vary somewhat in theamounts of the various constituents, e. g. expressed as percentages:carbon 0.25-0.32; manganese 1.6-1.0; sulfur 0.04 maximum; phosphorus0.04 maximum; silicon 0.2-0.3; molybdenum 0.4-0.5, and rare earth metal0003-0009, the remainder being iron.

The method herein described for the production of iron and steel leadsto the formation of a fine grain structure which enhances the resistanceto corrosion. Since there is only a small amount of the L-metalremaining in the treated metal, it is believed that this condition isdue to the small space between the grains which results from thereduction of the original dendritic structure and, hence, offers lessinterstitial space for attack.

The results show that there are several advantages which accrue to theuser of L-metal when utilized in the manner described herein. Thus, onemay use a standard material and obtain decided benefits due to itsresistance to corrosion and oxidation. Further, the analysis may bevaried so that less of a scarce and costly alloy will be employed toobtain the same results as the same untreated material with a largeramount of the alloy.

In the melting and casting of the iron and steel, certain precautionshave been found to be beneficial and are recognized as being properpractice. For instance, a good pouring temperature would be about 2700F. We have also found that the melt, after treatment in the ladle,should be poured immediately to insure quick freezing of the metal, andin some instances a thick walled ingot mold serves to effect the quickfreezing. Due to the fact that slags cause reaction at the point ofcontact with the metal, it has been found that chilling the slag reducessuch action, and this may be accomplished by the addition of slag makingmaterials such as dolomite, burnt lime, and the like. Among theadvantages attending the use of L-metal, are a reduction of the sulfurcontent and the obtention of a fine grain as cast. These occasion higherimpact values at room and at low temperatures, and such values areespecially valuable in those types of steel which must function properlyand safely at low temperatures, e. g. those in the arctic and antarcticregions.

Further, when molten ferrous material has been treated with L-metal, ora metal made from a combination of rare earths, a fine grain results andlater certain definite improved physi-'- cal and chemicalcharacteristics are obtained. When steels are made in this way, it ishighly desirable to make the steel so that this fine grain,

as cast, persists. This is accomplished by casting at a relatively lowtemperature, e. g. at temperatures from about 2710 F. to about 2780 F.and tapping or teeming as quickly as possible to solidify the material.

W e have observed that if, after treatment with a substance which willendow it with these fine grain properties, the metal is allowed toremain in a liquid state for a long period of time, the fine graingradually disappears and the resultant metal compares in almost everyway with untreated metal. Thus, when a melt is treated with L-metal andsubsequently cast, as a sand casting, whose solidification rate is veryslow, a very small reduction in the grain size is obtained whichindicates that retention for a long time after treatment in a liquidstate allows the force which produces the fine grain to be dissipatedand, hence, the line grain qualities are not attained.

A distinctive characteristic of this treatment is that only a smallamount of the rare earth metal is used, and this is such that analysisof the finished steel shows that the quantity added is no longerexistent and that the quantity present is not greater than 0.018%, e. g.cerium. The rare earth metal content desirably may range from about0.003% to about 0.009%, and suitably will be about 0.005%. Thisindicates that it is not the presence of an alloy which confers thisfine grain property but rather an effect which is considered to inducenucleation.

Metallurgical examination of the results of the treatment or" liquidferrous material with L- inetal leads to the belief either that the Lmetal is oxidized, or that it forms a compound with some of thenon-metallics or with occluded gases which offer nuclei forcrystallization similar to the result of adding titanium to aluminum,whereby a fine grain is obtained.

It may be added, somewhat by way of recapitulation, that a steel havinga tendency ordinarily to solidify in large dendrites, has a much smallergrain size as cast than the untreated metal. This finer grain sizeincreases resistance to corrosion, and. gives a relatively high impactvalue at room and at low temperatures.

Furthermore, the addition, as above indicated, of a rare earth metaleither singly or in compatible admixture effects a reduction in thesulfur content, and such reduction results in enhanced physicalproperties and distinctive cleanliness in the product.

Since certain changes in carrying out the above process, and certainmodifications in the product which embody the invention may be madewithout departing from its scope, it is intended that all mattercontained in the above description shall be interpreted as illustrativeand not in a limiting sense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed, and all statements of the scope of the invention which, as amatter of language, might be said to fall therebetween.

Having described our invention, what we claim as new and desire tosecure by Letters Patent is:

l. A method for the production of iron and which comprises preparing aniron containing melt, adding metallics thereto during furnacing,deoxidizing, incorporating a composition containing a rare earth metal,in an amount not more than three pounds per ton, pouring and quickfreezing.

2. A method for the production of iron and steel which comprisespreparing an iron containing melt, adding metallics thereto duringfurnacing, deoxidizing with the addition, and in conjunction therewith,of a composition containing a rare earth metal, in an amount not morethan three pounds per ton, pouring and quick freezing.

3. A method for the production of iron and steel which comprisespreparing an iron containing melt, adding metallics thereto duringfurnacing, deoxidizing, incorporating a composition containing aplurality of rare earth metals, in an amount not more than three poundsper ton, pouring and quick freezing.

4. A method for the production of iron and steel which comprisespreparing an iron containing melt, adding metallics thereto duringfurnacing, deoxidizing with the addition, and in conjunction therewith,of a composition containing a plurality of rare earth metals, saidcomposition containing cerium in a preponderant amount, in an amount notmore than three pounds per ton, pouring and quick freezing.

5. A method for the production of iron and steel which comprisespreparing an iron containing melt, adding metallics thereto duringfurnacing, deoxidizing substantially completely, then adding acomposition containing a plurality of rare earth metals, saidcomposition containing cerium in a preponderant amount, and being addedin an amount not more than three pounds per ton, pouring and quickfreezing.

6. A method for the production of iron and steel which comprisespreparing an iron containing melt, adding metallics including a memberof the group consisting of chromium, molybdenum, manganese, nickel,columbium, titanium, tantalum, cobalt, zirconium and silicon theretoduring furnacing, deoxidizing, adding a composition containing a rareearth metal to the ladle in an amount not more than three pounds perton, pouring and quick freezing.

7. A method for the production of iron and steel which comprisespreparing an iron containing melt, adding metallics including a memberof the group consisting of chromium, molybdenum, manganese, nickel,columbium, titanium, tantalum, cobalt, zirconium and silicon theretoduring furnacing, deoxidizing, adding a composition containing a rareearth metal to the ladle during pouring, and while the ladle is lessthan one-half full, in an amount not more than three pounds per ton,pouring and quick freezing.

8. An art cle of manufacture, a steel characterized by a fine grainstructure, substantial freedom from dendrites, resistance to corrosion,a relatively high impact value at low temperatures, capable of beingdirectly rolled to billet size and having the following approximatecomposition expressed as percentages: carbon 0.25- 0.32; manganese1.6-1.9; sulfur 0.04 maximum; phosphorus 0.04 maximum; silicon 0.2-0.3;molybdenum 0.4-0.5; and rare earth metal 0.003- 0009, the remainderiron, said steel being produced by the method defined in claim 1.

9. An article of manufacture, a steel characterized by a fine grainstructure, substantial freedom from dendrites, resistance to corrosion,a relatively high impact value at low temperatures, capable of beingdirectly rolled to billet size and having the following approximatecomposition expressed as percentages: carbon 0.25- 0.32; manganese1.6-1.9; sulfur 0.04 maximum; phosphorus 0.04 maximum; silicon 0.2-0.3;

mee'smei 7 molybdenum 0.4-0.5; and rare e'arth met-a1 0.005, Number theremainder iron, said steel being produced by 1,892,044 the methoddefined 'in claim 7. 2,360,717

10. As an article of manufacture, a steel as defined in claim 8, said-steel being produced by 5 the method defined in claim 3. 2 3:; 8

References Cited in the file of this patent UNITED STATES PATENTS Number3 Name Date Eldred et a1. e Dec. 27, 1932 Phelps Oct. 17, 1944 FOREIGNPATENTS Country Date France Dec. 27, 1943 OTHER REFERENCES 10 Making,Shaping and Treating of Stee1, 6th edition, page 575. Published in 1951by the U. S. Steel Co., Pittsburgh, Pa.

1. A METHOD FOR THE PRODUCTION OF IRON AND STEEL WHICH COMPRISESPREPARING AN IRON CONTAINING MELT, ADDING METALLICS THERETO DURINGFURNACING, DEOXIDIZING, INCORPORATING A COMPOSITION CONTAINING A RAREEARTH METAL, IN AN AMOUNT NOT MORE THAN THREE POUNDS PER TON, POURINGAND QUICK FREEZING.